Acceleration sensors are used within vehicles to control systems responsive to acceleration of the vehicle or responsive to acceleration of a component of the vehicle. For example, an acceleration sensor is used to sense acceleration which is indicative of a vehicle collision. One or more vehicle occupant restraint devices, such as air bag modules and seat belt pretensioners, are controlled in response to the sensed acceleration.
Another example of the use of an acceleration sensor in a vehicle is within an active suspension system of the vehicle. Acceleration of a sprung mass (e.g., the vehicle body) is sensed by the acceleration sensor. A hydraulic actuator is controlled in response to the sensed acceleration to enhance vehicle suspension performance.
It is possible to assess the condition of at least one type of acceleration sensor by electrically exciting the acceleration sensor, and thereby produce a response at the sensor's output. For example, one type of acceleration sensor is a capacitance-based accelerometer which has a seismic mass. The seismic mass moves in response to acceleration and also moves in response to electrical excitation. An electrical output signal is provided by the accelerometer in response to movement of the seismic mass. The capacitance-based accelerometer is tested by moving the seismic mass via an applied test (i.e., known) excitation and analyzing the output signal to see if an expected result occurs.
Often, acceleration sensor systems are mass-produced in large quantities. The large quantities correspond to the large quantities of vehicles within which the acceleration sensor systems are used. One type of acceleration sensor system which is often mass-produced has structure for testing its acceleration sensor without the aid of external equipment (i.e., the system performs a "self-test" on its acceleration sensor). A self-test acceleration sensor system can self-test its acceleration sensor as frequently as desired.
One approach used for self-test acceleration sensor system production is to configure all of the produced systems to have a standard (i.e., identical) test excitation. Unit-to-unit variation may occur among the outputs of several acceleration sensors in response to a standard self-test excitation despite the fact that all of the acceleration sensors are properly functioning.